Drilling a hole in soil is generally accomplished with a drill bit. Drill bits may also be configured to directionally drill holes within soil. The drill bit digs the soil and then the soil is conveyed up and out of the bore. It is difficult to drill in unstable soil. Many difficulties are raised by drilling in unstable soil. One of the difficulties is that the unstable soil tends to impede the drill bit. Also, it is difficult to convey the unstable soil out the hole as it is being drilled. Further complicating matters is that after the hole is drilled in unstable soil it has a tendency to collapse.
Unstable soils, such as gravel, are often found adjacent to rivers or streams. Thus, directionally drilling is not typically an option available when it is desired to place a bore underneath a river or stream.
In the prior art, pipe was placed in soil by first digging a trench and placing the pipe within the trench. This technique worked well for both stable and unstable soils. However, digging a trench and placing a pipe within it has many disadvantages, not the least of which is that the technique is extremely costly and time consuming.
Digging a trench is a known technique of the prior art to place pipe underneath rivers or streams. To dig a trench under a river or stream, the river or stream must be dammed up to permit backhoes to access the area for digging. If the river or stream is very deep or wide, it may have to be partially dammed so that trenches may be dug on opposite sides of the river. Further, environmental regulations restrict work on placing a pipe underneath a waterway to narrow windows of time. For example, environmental regulations often forbid work when fish are spawning, or during fishing season. Also, the location of the pipeline may be restricted as not to disturb environmentally fragile spawning grounds. All of the difficulties associated with placing pipe underneath a river extend the time it takes to place pipe under such circumstances to a year or more.
Pipes may be placed in stable or unstable soils without digging a trench by ramming the pipe into the soil and then clearing the soil from the pipe with, for example, compressed air. This is generally known as "trenchless" pipe placement. However, such "trenchless" placement of pipes may only be accomplished in a straight line. Thus, problems exist when the pipe which is to be placed is not intended to move in a straight line. Line, for example if it is desired to place a pipe underneath a river or within a metropolitan area.
There are many different types of pipe rammers. Pipe rammers typically ram pipes directly into soil. An example of a pipe ramming machine is described in U.S. Pat. No. 5,289,887 entitled "Method of Operating an Earth Boring Machine." This machine operates by directly ramming pipe into soil with pneumatic power and clearing soil from the pipe.
When ramming pipe the prior art provides that a cutting shoe may be positioned on the outside of the tube. The cutting shoe is slip fit to the outside of the pipe and held to the pipe by deformation of the shoe. The shoe and pipe combination is designed such that the soil is forced into the lumen of the tube as it is rammed. The soil is then removed from the lumen of the tube and the pipe is put in use.
A need exists to improve the placement of pipe in difficult areas. A need also exists to permit direction drilling in unstable soils.